[dev.power64] cmd/dist: recognize power64 and power64le as GOHOSTARCH
[dev.power64] cmd/dist: recognize power64 and power64le as GOHOSTARCH

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/125760043

webfd/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,d0f/go-zh,d0f/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh